1. Field of the Invention
The invention relates to the use of nordihydroguaiaretic acid derivatives, in particular derivatives containing substituents of naturally occuring amino acids, for the treatment of tumors and viral infections.
2. Background Information
Carcinogenesis is a multistage event affected by a variety of genetic and epigenetic factors and is typified by the outbreak of uncontrolled cell growth originated from different tissues. A universal goal for anticancer research lies in the development of a clinical treatment that is highly effective in curtailment of tumor growth, non-toxic to the host, and is affordable for most patients. Drugs that focus on the inhibition of targets that are unique to dividing cells should be effective chemotherapeutic agents without the risk of substantial side effects.
Cells pass through many checkpoints as they proceed through the cell cycle. Certain criteria must be met in order to pass each of these checkpoints. In the G2/M transition, the most essential regulator is the cyclin-dependent kinase CDC2. This kinase binds tightly to the regulatory protein cyclin B, and this complex, also called the maturation promoting factor (MPF), is responsible for stimulating a myriad of events that lead to the cell's entry into early prophase (1). Not surprisingly, the loss or deactivation of either component of the MPF will block cellular progression out of G2.
The expression and activity of the MPF is regulated at different levels. Cyclin B protein levels slowly rise through the G1 and S phases of the cell cycle, peak during the G2 to M phase transition, and drop sharply during mitosis (2). The CDC2 protein, on the other hand, is always present during the cell cycle, although levels rise slightly in the last stages of the G2 phase (3). The activity of the protein is dependent on the association with the appropriate cyclin, as well as on the dephosphorylation of its inhibitory sites by the phosphatase CDC25C (4,5). It has been shown that the failure of this dephosphorylation initiates G2 arrest in response to DNA damage by radiation or chemical action. Recent evidence also suggests that any remaining active CDC2 may be transported outside the nucleus following DNA damage (6).
A number of naturally occurring derivatives of the plant lignan nordihydroguaiaretic acid (NDGA) have been shown to block viral replication through the inhibition of viral transcription. This earlier work has shown that NDGA derivates, originally isolated from Larrea Tridentata and subsequently synthesized chemically, can inhibit the production of HIV (7,8), HSV (9), and HPV transcripts (10) by the deactivation of their Sp1-dependent promoters. Unexpectedly, one of these derivatives, tetra-O-methyl NDGA, appears to also induce cell cycle arrest in mammalian cell lines. The evidence presented hereinbelow demonstrates that M4N is capable of inducing G2 arrest in mammalian cells without detected toxicity, and supports the view that this arrest is due to the inhibition of the cyclin-dependent kinase CDC2.
Human papillomavirus (HPV) infection causes unregulated cell growth in many types of squamous epithelial cells, resulting in afflictions ranging from benign pallilomae (warts) to cervical, penile and mouth cancer. The strong association of these cancers with HPV and the widespread occurrence of infection denotes the importance of developing an anti HPV therapy.
Most, if not all, viruses, including those replicatively active mutants, are host dependent. They require the participation of certain cellular factors for supporting viral growth. Host cellular factors, unlike viral proteins, are not under mutational pressure and are in general, structurally invariable. Thus, compounds that block the usage of these cellular factors at different stages of the viral life cycle are likely to be good candidates as mutation insensitive antiviral drugs. Several studies using cellular factors as alternative targets for the inhibition of HIV-1 have been reviewed (11).
Applicants reported earlier that 3′-0-methylated NDGA (i.e. Mal.4), isolated from Creosote bush (Larrea tridentata) can specifically block basal HIV transcription, Tat-regulated transactivation, and HIV replication in human cell culture (12,13,14). Mal.4 exerts its effects by interfering with the binding of transcription factor Sp1 to the promoter of the HIV proviral template. The target of Mal.4 is mapped to nucleotides −87 to −40, the Sp1 binding sites of the HIV long terminal repeat (LTR). The unmodified NDGA, in vitro, does not inhibit HIV transcription and has no effect on Sp1 binding (12).
Isolation and purification of plant lignans, however, is labor intensive and costly. In anticipation of the possible clinical use of plant lignans in controlling Sp1-regulated viral and tumor growth in humans, nine different methylated NDGA activities were synthesized chemically using unmethylated NDGA as the parent substrate in large quantities with low cost (15). At drug concentrations below 30 μM, tetra-O-methyl NDGA was found to be most effective in the control of replication HIV via inhibition of Sp1 regulated proviral transcription and transactivation (15). This study has since been extended to the control of the growth of Herpes simplex virus (HSV-1 and HSV-2) (16). Herpes simplex immediate early (IE) ICP4 gene is essential for HSV replication (17). Its promoter region possesses eight Sp1 consensus binding sites (18), five of which are required for ICP4 gene expression. It thus makes the ICP4 gene a good candidate for such testing. Applicants have found that both 3-0-methyl NDGA (Mal. 4) and tetra-O-methyl NDGA (M4N) are effective transcriptional inhibitors for HSV ICP4 gene expression in Vero cells via the blocking of Sp1 protein binding to the ICP4 promoter as shown by the electrophoretic mobility shift assay (16).
When the anti-HSV activities of M4N and Mal. 4 were tested and compared to that of acycloguanosine (acyclovir, ACV) in infected Vero cells, Applicants observed that the IC50 for M4N varied between 11.7 μM to 4 μM for 10 passages of HSV-1 and 4 passages of HSV-2 without obvious uprising trend for requirement of higher drug concentration. However, the IC50 for ACV increased from 7 μM for the first viral passage to 444 μM for the tenth passage of HSV-1 and to >88 μM for the fourth passage of HSV-2 indicating their rapid build-up of drug resistance against ACV in Vero cells. Consequently, while the selective index, S.I. (TC50/IC50) remained relatively stable for M4N, the S.I. for ACV dropped 60 fold following the viral passages in Vero cells (16). Thus M4N is a mutation insensitive drug. It can inhibit ACV resistant HSV effectively (16).
Due to the fact that Sp1 is an important cellular transcription factor (19), the possible inhibitory effect of this class of compounds on the expression of Sp1-regulated cellular genes should be addressed. Mal.4 cannot displace Sp1 once it is stably bound to its binding sites (12). It therefore seemed likely that NDGA derivatives would have a greater effect on Sp1 -regulated genes in proliferating cells than on the expression of Sp1-regulated housekeeping genes in stationary cells. In the former case, the drug will be able to compete with Sp1 protein for the Sp1 sites in gene promoters during DNA synthesis, while in the latter case, the drug may have little effect on the transcribing chromatin of housekeeping genes with Sp1 protein already stably bound at their promoters. This, in fact, has been shown to be the case. As will be demonstrated below, by using gene array studies with 9600 expressed genes, Applicants found products of most Sp1 regulated genes remained at similar levels, and not affected by the drug treatment of cervical cancer cells C3 in culture (FIG. 5). Even so, the relatively low selective index of M4N certainly limits its use to the lowest effective concentration if the drug must be used systemically. On the other hand, human papilloma virus induces solid cervical and oral tumors initially through the Sp1 regulated expression of HPV E6/E7 genes (20). Applicants reasoned that if drug can be delivered in situ, and be kept only in the tumor area, the drugs of high concentration may be used to effectively destroy the tumor with little damage to the patients.